1. Field of Invention
This invention relates to electrochemical reference electrodes, and in particular, reference electrodes which are used in potentiometric measurements of the activity of ions in solution.
2. Prior Art Statement
Electrochemical reference electrodes with liquid junctions between the internal electrolyte and the external sample solution are well known in the art as illustrated in U.S. Pat. No. 2,705,220 issued Mar. 29, 1955 to Edward P. Arthur. The general technique of providing a leak structure which permits a controlled flow of electrolyte to sample solution has been the object of liquid junction design for over two decades. Specific liquid junction designs generally recognize that the useful life of reference electrodes is limited by the contamination of the internal electrolyte from inward migration of sample solution through the liquid junction, and by the destruction of the electrical contact between electrolyte and sample solution due to clogging of the liquid junction structure by solids or viscous materials in the sample solution.
Contamination of the internal electrolyte has been controlled by pressurization, as illustrated by U.S. Pat. No. 3,455,793 issued July 15, 1969 to H. Watanabe and E. E. Buzza. Methods similar in principle have been developed in which a constant outflow of electrolyte through the liquid junction shows contamination. These techniques require replenishment of electrolyte throughout the life of the electrodes.
A design which eliminates the clogging problem is illustrated in U.S. Pat. No. 3,486,997 issued Dec. 30, 1969 to Arne J. Petersen. Here, the liquid junction is formed by a valve body positioned within a tube which terminates in an inwardly extending flange providing a central opening in the end of the tube. The valve body includes an enlarged portion positioned inside and freely movable within the tube adjacent to the flange, and a smaller portion protruding through the opening and extending beyond the end of the tube. The body cooperates with the inner surface of the flange to provide a minute passageway through the end of the tube. This design allows the valve body to be moved inwardly by exerting pressure on the protruding portion, so that clogging materials can be flushed out of the liquid junction. However, the Petersen device does not eliminate the contamination problem since inward migration from the test solution is not restricted when the reference electrode is in normal use.
The present invention is designed to eliminate the contamination and clogging problem. An additional benefit includes self-replenishment of electrolyte, thus eliminating the danger of dry-up and increasing the efficiency and lifetime of the reference electrode use.